<form id="order">
   <input type="text" name="name" required />
   <input type="submit" id="submit" />
form>

<script>
   $("#order").submit(function(){
      event.preventDefault(); //不写的话， 会提交两次
      $.ajax({
        ...
     })
   });
script>

错误代码如下:

<form id="order">
   <input type="text" name="name" required />
   <input type="submit" id="submit" />
form>

<script>
   $("#submit").bind("click",function(){
      $.ajax({
        ...
     })
   });
script>